Light-Assisted Catalytic Water Oxidation from Porphyrin J-Aggregate

For photoelectrochemical splitting of water into hydrogen and oxygen, the main challenge is to ensure that the photogenerated holes can efficiently oxidize water before recombination. An oxygen evolution catalyst is necessary to increase the photocurrent and reduce the onset potential. Most molecular water-oxidation catalysts studied thus far are transition-metal complexes. Herein we report the light-driven electrochemical water oxidation by the porphyrin J-aggregate. Oxygen generated from water was detected at the presence of Ag+ severing as the electron sacrificial agent. The catalytic activity of the metal-free porphyrin J-aggregate is deduced to be originated from the long-standing charge separation upon visible-light illumination. The Proton-Coupled Electron Transfer (PCET) mechanism involving H-bonding of water molecules to the free porphyrin base is suggested for the water oxidation reaction. These findings offer a new sight in photocatalytic activity of the porphyrin assembly as well as its functionalization in light energy conversion.